Ulcerative colitis (UC) is a chronic mucosal inflammation which can affect any parts of colon but rectum is involved in the most of the cases. This disease characterized by bloody diarrhea, colicky abdominal pain, urgency and tenesmus.The main pathogenesis of this disease is already unknown. Many studies are focused on the role of abnormal mucosal immune responses to enteric bacteria triggered by environmental Factors. We conducted a randomised clinical trialPatients who took NSAIDs, vasodilators, corticosteroids (some studies showed they might affect tissue oxygenation) and patients with past medical history of ischemic heart disease, pulmonary disorders (COPD, asthma), severe anemia and vascular disease ( vasculitis) and Diabetes which can cause tissue hypoxia were excluded. study to assess the role of ischemia in UC. 20 patients with UC, 20 people without any history of bowel disease and ten paraffin wax embedded tissue species from mesenteric ischemia and ten paraffin wax embedded tissue species include infectious colitis entered the study. Patient group underwent colonoscopy and endoscopy. Three samples were taken from the colon; one from ulcerative tissue, one from normal intestinal tissue and the last one from body of the stomach. Endoscopy and colonoscopy were also done for control group (they had referred for screening) with preparing one sample from colon and another from body of stomach. Systemic arterial blood gas sampling (ABG) was performed from radial artery after Allen testing. More over, perirectal capillary blood gas analysis using endoscopic ultrasound (EUS) with 100 cc normal saline and 80 mg gentamycine enema immediately before the procedure was performed. Thirty minutes after perirectal capillary blood gas was taken, blood culture was done to rule out bacteremia. Pathological species transferred to department of pathology for measuring HIF1a. Blood gas samples were assessed within 5 minutes in laboratory by pathologist, and results were recorded.Statistical analysis was done by the SPSS Statistics Data Document. (V 19.2) Differences among groups were determined using the general repeated ANOVA.